1. Field of the Invention
This invention relates generally to a micro-circuit cooling module for providing endwall cooling for a vane assembly in a gas turbine engine and, more particularly, to a micro-circuit cooling module for providing endwall cooling for a vane assembly in a gas turbine engine, where the micro-circuit cooling module includes criss-crossing channels providing a turbulated cooling air flow.
2. Discussion of the Related Art
The world's energy needs continue to rise which provides a demand for reliable, affordable, efficient and environmentally-compatible power generation. A gas turbine engine is one known machine that provides efficient power, and often has application for an electric generator in a power plant, or engines in an aircraft or a ship. A typically gas turbine engine includes a compressor section, a combustion section and a turbine section. The compressor section provides a compressed air flow to the combustion section where the air is mixed with a fuel, such as natural gas, and ignited to create a hot working gas. The working gas expands through the turbine section and is directed across rows of blades therein by associated vanes. As the working gas passes through the turbine section, it causes the blades to rotate, which in turn causes a shaft to rotate, thereby providing mechanical work.
The temperature of the working gas is tightly controlled so that it does not exceed some predetermined temperature for a particular turbine engine design because to high of a temperature can damage various parts and components in the turbine section of the engine. However, it is desirable to allow the temperature of the working gas to be as high as possible because the higher the temperature of the working gas, the faster the flow of the gas, which results in a more efficient operation of the engine.
In certain gas engine turbine designs, a portion of the compressed air flow is also used to provide cooling for certain components in the turbine section, typically the vanes, blades and ring segments. The more cooling and/or the more efficient cooling that can be provided to these components allows the components to be maintained at a lower temperature, and thus the higher the temperature of the working gas can be. For example, by reducing the temperature of the compressed gas, less compressed gas is required to maintain the part at the desired temperature, resulting in a higher working gas temperature and a greater power and efficiency from the engine. Further, by using less cooling air at one location in the turbine section, more cooling air can be used at another location in the turbine section. In one known turbine engine design, 80% of the compressed air flow is mixed with the fuel to provide the working gas and 20% of the compressed air flow is used to cool the turbine section parts. If less of that cooling air is used at one particular location as a result of the cooling air being lower in temperature, then more cooling air can be used at other areas in the turbine section for increased cooling.
Backside impingement in conjunction with multiple rows of film cooling is employed in some turbine designs for providing high temperature first vane endwall cooling. Compartments are employed on the back side of the endwall for better control of cooling flow and pressure distribution. However, for a fixed impingement pressure across the impingement holes or post impingement cooling air pressure, each individual compartment experiences large main stream pressure-to-cooling air pressure variations. In addition, each impingement compartment needs to provide a post impingement pressure that is higher than the maximum main stream hot gas pressure in order to achieve a good black flow margin (BFM). Consequently, there is typically an over-pressure at the lower main stream hot gas pressure location. This over-pressure becomes more profound at the aft portion of the vane suction side (SS), where the endwall sees the maximum main stream variation as well as a maximum cooling air to hot gas pressure ratio. Extensively metering the cooling pressure through the impingement holes in order to obtain the maximum film cooling on the endwall surface may result in a hot gas ingestion problem when some of the impingement holes are plugged by dirt or other debris. As a result of this large compartment cooling construction, it is sometimes difficult to achieve a stream-wise and circumferentially-wise cooling flow control for a vane endwall with large external hot gas temperature and pressure variations. In addition, a single impingement cooling technique having a large impingement cavity to cover a large endwall region is generally not the best method for employing cooling air. The resulting mal-distribution of cooling flow yields low convective cooling effectiveness.